Epstein Barr virus (EBV) is the cause of infectious mononucleosis and is associated with a number of cancers including lymphomas in transplant recipients. We have been studying EBV DNA in the blood of transplant recipients, chronic active EBV disease, and in patients with other immunocompromising diseases. Multiple sclerosis is a disease of the central nervous system; multiple serologic studies have shown higher levels of antibodies to EBV in the serum before the onset of multiple sclerosis in patients 25 years or older. We collaborated with Jan Lunemann and Roland Martin, formerly of the National Institute of Neurologic Disorders and Stroke, to study patients with multiple sclerosis. Dr. Lunemann?s group found elevated levels of specific lymphocytes (memory CD4 cells) directed against an EBV nuclear protein with increased ability to proliferate in patients with multiple sclerosis compared with healthy EBV-seropositive controls. Also the patients with multiple sclerosis had lymphocytes that responded to a large portion of the EBV nuclear protein, while the healthy carriers responded to a very narrow region of the protein. We measured EBV DNA viral loads and found no significant difference in the level of viral DNA in patients with multiple sclerosis compared with EBV-seropositive controls, indicating that the patients were able to effectively control levels of EBV in the blood.